Efficient sacrificial reagent free (and no external bias) photoelectrochemical CO 2 reduction to formate with a hybrid system consisting of semiconductor-based photocatalytic TiO 2 nanoparticles, methylviologen (MV) as an electron carrier, and biocatalytic formate dehydrogenase (FDH) was investigated. To develop the sacrificial reagent free photoelectrochemical cell for the CO 2 reduction to formate, the photoanode based on TiO 2 film and cathode based on the carbon fabric paper (CFP) were separated into two compartments using a protonpermeable Nafion film to prevent gas diffusion. When the anode was irradiated with Xenon lamp (> 300 nm), MV reduction and CO 2 reduction to formate with FDH on the cathode side proceeded in this system. For MV reduction with photoelectrochemical cell, MV was reduced using TiO 2 film at each pH (6, 7 and 8) without bias, the reduction of MV did not progressed at pH 6. In contrast, MV reduction was progressed at pH 7 or 8. For CO 2 reduction to formate in the presence FDH on the cathode side with photoelectrochemical cell, the rate of formate production was estimated to be 31.9 nmol h À 1 at pH 8 under continuous irradiation without bias. Moreover, the rates of formate production at pH 7 and 8 were estimated to be 56.5 and 168.8 nmol h À 1 , respectively under continuous irradiation with bias (0.4 V vs. cathode). By using this system, we have succeeded in constructing CO 2 reduction to formate using water as an electron donor, which does not require a sacrificial reagent.[a] T. Figure 1. Formic acid-CO 2 conversion catalyzed with FDH in the presence of natural co-enzyme NAD + /NADH redox coupling.
The kinetic properties of formate reduction to formaldehyde with formaldehyde dehydrogenase (FldDH) using single-electron reduced methylviologen (MV˙) as a co-enzyme were clarified.
The Cover Feature shows a photoelectrochemical CO2 reduction to formate with the sacrificial reagent free system of semiconductor photocatalyst and biocatalyst. In their Full Paper, Shigeru Ikeda, Yutaka Amao and co‐workers demonstrate that light‐driven CO2 reduction to formate with the hybrid system of photoanode based on TiO2 film and cathode based on the carbon fabric paper in the presence of methylviologen as an electron mediator and formate dehydrogenase on the cathode side. By using this system, the authors have succeeded in developing CO2 reduction to formate using water as an electron donor, which does not require a sacrificial reagent. The results open a new avenue for the innovative light‐driven CO2 reduction with photo/biocatalysts hybrid system. More information can be found in the Full Paper by Tomoya Ishibashi et al. on page 6227 in Issue 24, 2019 (DOI: 10.1002/cctc.201901563).
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